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madura96's solution

to Matrix in the Java Track

Published at Oct 12 2019 · 0 comments
Instructions
Test suite
Solution

Given a string representing a matrix of numbers, return the rows and columns of that matrix.

So given a string with embedded newlines like:

9 8 7
5 3 2
6 6 7

representing this matrix:

    1  2  3
  |---------
1 | 9  8  7
2 | 5  3  2
3 | 6  6  7

your code should be able to spit out:

  • A list of the rows, reading each row left-to-right while moving top-to-bottom across the rows,
  • A list of the columns, reading each column top-to-bottom while moving from left-to-right.

The rows for our example matrix:

  • 9, 8, 7
  • 5, 3, 2
  • 6, 6, 7

And its columns:

  • 9, 5, 6
  • 8, 3, 6
  • 7, 2, 7

Setup

Go through the setup instructions for Java to install the necessary dependencies:

https://exercism.io/tracks/java/installation

Running the tests

You can run all the tests for an exercise by entering the following in your terminal:

$ gradle test

Use gradlew.bat if you're on Windows

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by removing the @Ignore("Remove to run test") annotation.

Source

Warmup to the saddle-points warmup. http://jumpstartlab.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

MatrixTest.java

import org.junit.Ignore;
import org.junit.Test;

import static org.junit.Assert.assertArrayEquals;

public class MatrixTest {

    @Test
    public void extractRowFromOneNumberMatrixTest() {
        String matrixAsString = "1";
        int rowIndex = 1;
        int[] expectedRow = {1};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractRowFromMatrixTest() {
        String matrixAsString = "1 2\n3 4";
        int rowIndex = 2;
        int[] expectedRow = {3, 4};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractRowFromDiffWidthsMatrixTest() {
        String matrixAsString = "1 2\n10 20";
        int rowIndex = 2;
        int[] expectedRow = {10, 20};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractRowFromNonSquareMatrixTest() {
        String matrixAsString = "1 2 3\n4 5 6\n7 8 9\n8 7 6";
        int rowIndex = 4;
        int[] expectedRow = {8, 7, 6};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedRow, matrix.getRow(rowIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnFromOneNumberMatrixTest() {
        String matrixAsString = "1";
        int columnIndex = 1;
        int[] expectedColumn = {1};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnMatrixTest() {
        String matrixAsString = "1 2 3\n4 5 6\n7 8 9";
        int columnIndex = 3;
        int[] expectedColumn = {3, 6, 9};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnFromNonSquareMatrixTest() {
        String matrixAsString = "1 2 3 4\n5 6 7 8\n9 8 7 6";
        int columnIndex = 4;
        int[] expectedColumn = {4, 8, 6};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }

    @Ignore("Remove to run test")
    @Test
    public void extractColumnFromDiffWidthsMatrixTest() {
        String matrixAsString = "89 1903 3\n18 3 1\n9 4 800";
        int columnIndex = 2;
        int[] expectedColumn = {1903, 3, 4};

        Matrix matrix = new Matrix(matrixAsString);

        assertArrayEquals(expectedColumn, matrix.getColumn(columnIndex));
    }
}
class Matrix {

    Matrix(String matrixAsString) {
    	if(matrixAsString == null || "".contentEquals(matrixAsString)) {
    		throw new IllegalArgumentException("Given matrix must not be null nor empty");
    	}
    	
    	// parse the matrix string into its equivalent 2-dimensional integer matrix
        String[] lines = matrixAsString.trim().split("[\n]+");
        matrix = new int[lines.length][]; // allocate the lines array
       
        for(int i=0; i<lines.length; i++) {
        	String[] columns = lines[i].trim().split("[\\s]+");
        	
        	// the matrix must have the same number of columns in each row
        	if (i>0 && columns.length != matrix[0].length) {
        		throw new IllegalArgumentException("Given matrix " + matrixAsString + " does not have the same number of columns");
        	}
        	
        	matrix[i] = new int[columns.length]; // each sub-array must be allocated (one line with n columns)
        	 for(int j=0; j<columns.length; j++) {
        		 matrix[i][j] = Integer.valueOf(columns[j]);
        	 }
        }
    }

    int[] getRow(int rowNumber) {
        return matrix[rowNumber-1];
    }

    int[] getColumn(int columnNumber) {
    	int[] result = new int[matrix.length];
    	int j = 0; // column index
    	for(int line[] : matrix) {
    		result[j] = line[columnNumber-1];
    		j++;
    	}
    	return result;
    }
    
    int[][] matrix; // matrix is array of array of integers
}

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